1. Field of the Invention
The present invention relates to a distance detection apparatus and more particularly to a distance detection apparatus used for a photographic camera, a television camera or a robot.
2. Description of the Prior Art
Various types of distance detection apparatuses for detecting a distance to an object have been proposed, which detect the distance to the object to focus an imaging lens and used in the photographic camera a television camera. However, when in the case of the distance detection apparatus of, for example, a photographic camera, various objects are present at different distances from the distance detection apparatus. For example, when a mountain is present in a far background of a wide view field, houses are present in front of it and a human is present in front of the houses, an ordinary distance detection apparatus detects, in many cases, an average of the distances to those various objects. Assuming that the houses are at the average distance, the photographic image is focused to the houses and not focused to the human which a photographer wants to be in focus Such a problem is not limited to the distance detection apparatus of a photographic camera. For example, a device which detects a distance to an approaching object to issue an alarm is mounted in an automobile or an aeroplane in order to avoid collision. In such a device, a similar problem is encountered because the objects to be detected should be observed in a relatively wide view field. Thus, if the average distance of the distances to the objects in the view field is detected, a satisfactory result would not be obtained.
One method for resolving the above problem has been proposed in U.S. Pat. No. 4,475,800 assigned to the assignee of the present invention in which a portion of a view field in which an object to be detected is present is selected, that is, a narrow view field which contains only the object to be detected is selected so that the distances to objects not of interest are not detected. In this method, it is necessary to select the narrow view field in accordance with a position of the desired object in the view field and a complex step is required to select the narrow view field. In addition, a complex selection circuit is required. In certain cases, objects at different distances coexist and a definite selection is hard to attain. Accordingly, this method does not provide a complete resolution of the problem.